1. Field of the Invention
The present invention relates to a battery system using a number of battery cells.
2. Description of the Related Art
In a case where a number of battery cells such as hundreds of battery cells are used so as to generate a large output, such configuration that a plurality of battery packs are connected in series is employed. Such configuration is called a battery system. A battery pack is a unit obtained by assembling a plurality of battery cells and a controller. A battery pack MOD is configured as shown in FIG. 1. A controller CNT is provided to a battery unit BT in which a plurality of battery cells, for example, 16 battery cells (for example, lithium-ion batteries) are connected in series. The controller CNT outputs information of inside states such as a voltage, current, and a temperature of each of the cells of the battery unit BT. For example, one battery pack MOD outputs 16×3.5 V=56 V.
Further, as shown in FIG. 2, N pieces of battery packs MOD1 to MODN are connected in series. The battery packs MOD1 to MODN are connected to an interface bus BS via an insulating unit IS. To each of the battery packs MOD, an insulating interface IF is provided so as to connect the controller CNT and the interface bus BS which is externally provided, as shown in FIG. 1. This insulating interface IF insulates the battery pack MOD from the interface bus BS. The insulating unit IS shown in FIG. 2 collectively indicates the insulating interfaces IF of the battery packs MOD1 to MODN.
To the interface bus BS, a controller which controls the whole of the battery system (referred to below as an integrated controller) ICNT is connected. The controller CNT of each of the battery packs MOD communicates with the integrated controller ICNT. That is, the integrated controller ICNT receives information of the inside states of each of the battery packs MOD, and supplies and cuts off charging current and discharging current with respect to each of the battery packs MOD so as to control charge and discharge of each of the battery packs MOD. The integrated controller ICNT supplies an output (N×56 V) of the series connection of the N pieces of the battery packs MOD to a load. In an example of N=14, an output is 14×56 V=784 V.
Since the N pieces of the battery packs MOD are connected in series, as shown in FIG. 2, a basis voltage of the battery pack MOD1 on the lowest side is 0 V and a basis voltage of the battery pack MOD2 which is on the upper side of the battery pack MOD1 is 56 V. A basis voltage of the battery pack MODN on the highest side is 56 V×(N−1). In the example of N=14, the basis voltage is 56 V×13=728 V.
A specific connection of a battery system of the related art is shown in FIG. 3. An input signal from the integrated controller ICNT is supplied to an input terminal 1. A high level (Hi) of the input signal is +12 V and a low level (Lo) of the input signal is 0 V, for example. The battery packs MOD are respectively provided with photocouplers IF1 to IFN as the insulating interfaces IF. The battery packs MOD respectively include series regulators Reg1 to RegN, for example. Each of the photocouplers IF includes a light-emitting diode and a phototransistor which receives light from the light-emitting diode. The light-emitting diode emits light when the input signal is on the high level. The basis voltage of each of the battery packs MOD is supplied to an emitter of the phototransistor. A collector of the phototransistor is connected with an output terminal of each of the regulators Reg via a resistor.
The regulators Reg respectively generate input voltages (for example, reset voltages) with respect to the controllers CNT1 to CNTN from voltages of the battery units BT of the battery packs MOD. A direct-current voltage with respect to the controllers CNT1 to CNTN is +12 V with respect to the basis voltage. Output voltages of the regulators Reg1 to RegN are respectively extracted by output terminals 21 to 2N via transistors Tr1 to TrN. The controllers CNT1 to CNTN are respectively connected to the output terminals 21 to 2N.
When a high level input signal is supplied to the input terminal 1, the light-emitting diodes emit light and the phototransistors are turned on in the photocouplers IF1 to IFN. When the phototransistors are turned on, the transistors Tr1 to TrN are turned on and a high level output signal is generated with respect to the output terminals 21 to 2N. On the other hand, when the low level input signal is supplied to the input terminal 1, the light-emitting diodes do not emit light and the phototransistors are off in the photocouplers IF1 to IFN. Since the phototransistors are off, the transistors Tr1 to TrN are turned off and a low level output signal is generated with respect to the output terminals 21 to 2N.
The regulator Reg1 outputs a voltage of 12 V from a voltage of 56 V. Accordingly, when the transistor Tr1 is on, an output signal of Hi=12 V is generated, and when the transistor Tr1 is off, an output signal of Lo=0 V is generated. In the battery pack MOD1, a voltage up to 12 V is applied between an input side and an output side of the photocoupler IF1. In a similar manner, in the battery pack MOD2, the regulator Reg2 generates an output of 12 V+56 V=68 V from a voltage of 56 V+56 V=112 V. On the output terminal 22, an output signal of (Hi=12 V+56 V, Lo=56 V) is generated. In the battery pack MOD2, a voltage up to 68 V is applied between an input side and an output side of the photocoupler IF2.
In the battery pack MODN in the highest order, the regulator RegN generates an output of 12 V+56(N−1) V from a voltage of 56 V+56(N−1) V. On the output terminal 2N, an output signal of (Hi=12 V+56(N−1) V, Lo=56(N−1) V) is generated. In the battery pack MODN, a voltage up to 56(N−1) V is applied between an input side and an output side of the photocoupler IFN. In a case of N=14, for example, in the battery pack MODN in the highest order, a voltage up to (56×13+12 V=728 V+12 V=740 V) is applied to the photocoupler IFN.
A breakdown voltage of a common photocoupler is 500 V at most. If such photocoupler is used in a manner to be supplied with a voltage surpassing a rating, lives of elements may be extremely shortened and, at worst, problems such as a breakdown and ignition may occur.
FIG. 4 shows a second example of a battery system of the related art. Communication between the controllers CNT1 to CNTN of the inside of the battery packs MOD1 to MODN and the integrated controller ICNT is performed through a serial interface. Specifically, a system management bus (SM bus) or the like is used as the serial interface. For example, an I2C bus can be used. The I2C bus is a synchronous serial communication bus through which communication is performed with two signal lines of a serial clock (SCL) and bidirectional serial data (SDA). Further, a ground GND line is provided.
The battery packs MOD respectively include communication transceivers COM1 to COMN and bidirectional insulating buffers BF1 to BFN. The communication transceiver COM includes a transmission part Tx and a reception part Rx with respect to the signal line SDA and a transmission part Ty and a reception part Ry with respect to the signal line SCL, as shown in FIG. 5A. To each of the communication transceivers COM, a power source voltage of 12 V, for example, is applied from the integrated controller ICNT. Here, transmission/reception indicates transmission/reception of the controller CNT of the battery pack MOD.
As shown in FIG. 5B, the insulating buffers BF are integrated circuits (IC) which insulate a primary side (VDD1, SDA1, SCL1, and GND1) from a secondary side (VDD2, SDA2, SCL2, and GND2). For example, the insulating buffer BF is composed of a transformer of the IC configuration. The power source voltage VDD1 of the primary side of the insulating buffer BF is supplied from the controller CNT of each of the battery packs MOD and corresponding power source voltage VDD2 of the secondary side is supplied from the integrated controller ICNT. In order to form these power source voltages, regulators Reg11 to Reg1N and regulators Reg21 to Reg2N are provided.
For example, in the battery pack MOD1, the regulator Reg11 generates a power source voltage of 3.3 V from the voltage of 56 V which is received from the battery unit BT and the regulator Reg21 generates a power source voltage of 3.3 V from the voltage of 12 V. In the case of the battery pack MOD1, since basis voltages of the primary side and the secondary side of the insulating buffer BF1 are both 0 V, a voltage up to 0 V is applied between the primary side and the secondary side of the insulating buffer BF1.
In the battery pack MOD2, the regulator Reg22 generates a power source voltage of 3.3 V from the voltage of 12 V, as is the case with the regulator Reg21. On the other hand, the regulator Reg12 generates a voltage of 3.3 V+56 V from the voltage of 56 V+56 V of the battery unit BT of the battery pack MOD2. This is because the basis voltage of the battery pack MOD2 is 56 V. A voltage up to 56 V is applied between the primary side and the secondary side of the insulating buffer BF2.
In the battery pack MODN in the highest order, the regulator ReglN generates a voltage of 3.3 V+56(N−1) V from the voltage of 56 V+56(N−1) V. Accordingly, a voltage up to 0+56(N−1) V is applied between the primary side and the secondary side of the insulating buffer BFN. In the case of N=14, a voltage of 728 V is applied between the primary side and the secondary side of the insulating buffer BFN.
In a case of a common bidirectional insulating buffer, a breakdown voltage is 500 V at most. If such device is used in a manner to surpass a rating, a life of the device may be shortened and, at worst, a breakdown, smoking, ignition, or the like may occur.
A third example of the related art is described with reference to FIG. 6. A power-on signal from the integrated controller ICNT is inputted to an input terminal 10. The battery packs MOD1 to MODN respectively include photocouplers IF11 to IF1N and switching transistors Tr11 to Tr1N are respectively controlled by outputs of the photocouplers IF11 to IF1N.
Voltages of the battery units BT of the battery packs MOD are respectively supplied to emitters of the transistors Tr11 to Tr1N and the regulators Reg21 to Reg2N are respectively connected to collectors of the transistors Tr11 to Tr1N. Power-on signals of predetermined voltages from the regulators Reg21 to Reg2N are respectively extracted by output terminals 201 to 20N. The power-on signals are respectively supplied to the controllers CNT of the battery packs MOD. The controllers CNT which receive the power-on signals respectively start operations of the battery packs MOD.
In the battery pack MOD1, the voltage of 56 V is supplied from the battery pack BT to the emitter of the transistor Tr11. When a low level signal is supplied to a base of the transistor Tr11 from the photocoupler IF11, the transistor Tr11 is turned on. The voltage of 56 V is inputted into the regulator Reg21 via the transistor Tr11 and a power-on signal of 12 V is outputted to the output terminal 201.
Into the input terminal 10, a power-on signal of 12 V is inputted in power-on time, and a power-on signal of 0 V is inputted in power-off time. When the power-on signal is inputted into the photocoupler IF11, a light-emitting diode of the photocoupler IF11 emits light and a phototransistor is turned on in power-on time. Consequently, an output of the photocoupler IF11 becomes low level, for example, 1 V (a saturation voltage of the phototransistor). In this case, the transistor Tr11 is turned on. On the other hand, since the light-emitting diode does not emit light in power-off time, the output of the photocoupler IF11 becomes high level, for example, 56 V. In this case, the transistor Tr11 is not turned on and a power-on signal is not generated.
In the battery pack MOD1, the maximum value of a voltage which is applied between an input and an output of the photocoupler IF11 is 56 V. In the battery pack MOD2, the basis voltage is 56 V and the voltage from the battery unit BT is 56 V+56 V=112 V. Accordingly, the maximum value of a voltage which is applied between an input and an output of the photocoupler IF12 is 112 V. In the battery pack MODN in the highest order, the basis voltage is 0 V+56(N−1) V and the voltage of the battery unit BT is 56 V+56(N−1) V. Accordingly, the maximum value of a voltage which is applied between an input and an output of the photocoupler IF1N is 56(N−1) V. In the case of N=14, a voltage of 728 V is applied between the input and the output of the photocoupler IF1N.
In a case of a common photocoupler, a breakdown voltage is 500 V at most. If such device is used in a manner to surpass a rating, a life of the device may be shortened and, at worst, a breakdown, smoking, ignition, or the like may occur.
A fourth example of the related art is described with reference to FIG. 7. This example shows the configuration for extracting a state signal which is outputted from each of the battery packs MOD to an output terminal 21. The integrated controller ICNT is connected to the output terminal 21. As the state signal, OV, DIS, and CHG are shown. The state signal OV becomes low level when the battery unit BT of the battery pack MOD is overcharged. The state signal DIS becomes low level when the battery unit BT of the battery pack MOD is over-discharged. The state signal CHG becomes low level when a problem occurs while charging the battery unit BT of the battery pack MOD.
The battery packs MOD respectively include metal oxide semiconductor (MOS) field effect transistors (FET) Q1 to QN to which the state signal (one of the state signals OV, DIS, and CHG) is supplied to their gates. The MOSFETs Q1 to QN are n-channel type, so that the MOSFETs Q1 to Qn are turned on when a positive voltage is applied between a gate and a source. Light-emitting diodes of photocouplers IF21 to IF2N are respectively inserted between drains of the MOSFETs Q and output terminals of regulators Reg31 to Reg3N.
Collectors/emitters of phototransistors of the photocouplers IF21 to IF2N are connected in series. A predetermined direct-current voltage, for example, +12 V which is outputted from the integrated controller ICNT is supplied to a collector of the battery pack MODN. An emitter of the phototransistor of the photocoupler IF21 of the battery pack MOD1 on the lowest stage is connected to the basis voltage of 0 V via a resistor.
When a state signal becomes low level in any of the battery packs MOD1 to MODN, the MOSFET Q to which the state signal is supplied is turned from on to off. For example, if the state signal becomes low level in the battery pack MOD2, the MOSFET Q2 is turned from on to off. Accordingly, power feeding to the light-emitting diode of the photocoupler IF22 is cut off and the phototransistor of the photocoupler IF22 is turned off. Consequently, the voltage value of the output terminal 21 becomes 0 V.
When the state signals of all of the battery packs MOD1 to MODN are high level, the phototransistors of all of the photocouplers IF21 to IF2N are turned on and current flows to a resistor which is connected to the output terminal 21. Consequently, the voltage of the output terminal 21 becomes a predetermined positive voltage. The phototransistor has on resistance and, for example, voltage drop of 0.5 V occurs in one phototransistor. In the case of N=14, a sum of voltage drops is 7 V. Accordingly, a voltage of 12 V−7 V=5 V is generated on the output terminal 21.
A voltage which is applied to the photocouplers IF of the respective battery packs MOD is described. In the battery pack MOD1, a voltage up to 12 V−5 V=7 V is applied to the photocoupler IF21. In the battery pack MOD2, a voltage of (12 V+56 V)−5.5 V=62.5 V is applied to the photocoupler IF22. In the battery pack MODN in the highest order, a voltage of (12 V+56×(14−1) V)−12 V=728 V (in the case of N=14) is applied to the photocoupler IF2N.
In a case of a common photocoupler, a breakdown voltage is 500 V at most. If such device is used in a manner to surpass a rating, a life of the device may be shortened and, at worst, a breakdown, smoking, ignition, or the like may occur.
In the above-described configurations of the related art, the higher breakdown voltage of an insulating interface (a photocoupler or a bidirectional insulating buffer), which is disposed between the battery pack and the integrated controller, is demanded in the battery pack on the upper stage among the battery packs which are connected in series. Accordingly, the insulating interface has to be used while surpassing a rating. Japanese Unexamined Patent Application Publication No. 2009-100644 discloses an example of a battery system in which such problem does not arise.
In Japanese Unexamined Patent Application Publication No. 2009-100644, each battery pack includes a processing unit (microprocessor MPU), and the MPU communicates with a controller of a lower battery pack through a communication unit and communicates with a controller of an upper battery pack through an insulating unit and a communication signal. A voltage of a difference between upper and lower basis voltages is applied to the insulating unit, and therefore an insulating unit having a high breakdown voltage does not have to be used.